Avascular Necrosis

What is Avascular Necrosis (AVN) of the hip?

Bones are living tissues and so depend on a good supply of blood to keep them alive. If the blood supply is interrupted or restricted the bone tissue will begin to die causing the surrounding cartilage to deteriorate. Eventually the bone will collapse.

The picture on the right shows the head of a femur removed prior to hip replacement surgery. The flap at the top is a piece of cartilage which has loosened as a result of avascular necrosis

Avascular Necrosis is also known as osteonecrosis, asceptic (bone) necrosis and ischemic bone necrosis

Who does it affect?

Avascular necrosis can affect people of all ages and both sexes but is normally found in people between 30 and 60 years of age. The highest rate of incident being between 30 and 40. Avascular necrosis of the hip is one of the most common forms.

How many people are affected?

In the UK about 4,000 people are diagnosed with Avascular Necrosis each year.

Causes and Risks

Anything that causes a loss of blood supply to the bone.

Most commonly:-

Trauma or joint dislocation - it is now thought that 20% of people who dislocate their hip joint will later develop avascular necrosis

Steroid medication - studies show that 35% of the non-trauma related AVN cases are associated with long-term use of steroids.

Excessive alcohol use - it is believed that heavy drinking may result in fatty substances blocking crucial blood vessels .

Decompression - deep sea divers who work under great atmospheric pressure are at risk.

Symptoms

The first sign of AVN is pain when weight bearing. This is usually felt in the groin, buttock area and the front of the thigh. Other symptoms may develop as the condition progresses. These include stiffness in the joint and a limp. Eventually the pain may be experienced at rest and during sleep. The time between the onset of the first symptoms and the loss of joint function may be anything from a few months to more than a year. If the joint surface collapses pain may increase significantly. In some cases of hip avasacular necrosis osteoarthritis will develop.

Diagnosis

X-rays - in the early stages of the disease X-rays are unlikely to detect any changes as they are not sensitive enough. However they are useful for monitoring changes once the diagnosis has been established.

Bone Scan (scinitgraphy) - this is sometimes done after an initial X-ray turns out to be normal. A harmless, radioactive tracer is injected into the bone and shows up where normal bone formation is occurring. This type of scan is now being replaced by MRIs.

Magnetic Resonance Imaging (MRI) - MRI uses magnetic waves. It is very sensitive and can detect chemical changes in the bone marrow and pick up AVN in its earliest stages even before the patient is reporting symptoms. It is also a good way to monitor the bone rebuilding process after treatment has begun.

Functional Evaluation - this is a test to measure the pressure within the bone. It is very sensitive but seldom used as it requires surgery.

Treatment for Avascular Necrosis

Treatment will depend on a number of factors including how far the disease has progressed, the age of the patient and the underlying cause.

Medication - to reduce fatty substances (lipids) associated with corticosteroid use or to reduce blood clotting. Medication may also be prescribed to manage pain.

Physiotherapy - exercise may be prescribed to maintain and improve the range of motion of the joint. In addition the patient may be asked to decrease the amount of weight carried by the affected leg; either by limiting activities or using crutches. This may slow down any damage and allow healing to occur.

Femoral Osteotomy - is a surgical technique which realigns the bone to reduce stress. It is mostly used for patients with an advanced condition.

Core decompression - this is probably the most frequently performed procedure. One or more holes are drilled through the neck of the femur to the femoral head and plug/s of bone removed. This both relieves internal pressure and opens up channels for new blood vessels to form and thus re-establish the supply. Reducing the pressure should reduce the experience of pain.

Grafting - this involves moving bone, along with its blood supply, from the fibia (next to the shin bone) and implants this into a hole drilled into the femur. The blood vessels are then joined up to re-establish flow. The strong, boney graft also functions to stop the femoral head from collapsing.

Hip replacement - this is the usual treatment in the latter stages of the disease